Adhesive composition consisting of microcapsules containing compounds dispersed in a binder

ABSTRACT

An adhesive composition for being applied to at least one of thread contact faces of screw members so as to stick said thread contact faces to each other in engaging the screw members with each other for the purpose of locking and sealing the engaged screw members, in which micro-capsules enclosing at least a reactive monomer of a reactive adhesive composition comprising said monomer, a polymerization initiator of the aforesaid monomer and/or an activator of the aforesaid polymerization initiator is dispersed in a binder comprising a photo-hardening resin composition.

RELEVANT TECHNICAL FIELD

This invention relates to an adhesive composition for being applied tothe thread contact face (screw threads) of a screw member such as ascrew, bolt and nut for the purpose of locking and sealing up the screwmembers engaged with each other.

BACKGROUND OF THE ART

There have been conventionally known a variety of adhesive compositionsfor being applied to the thread contact face of a screw, bolt, nut orthe like for the purpose of locking and sealing up such screw membersengaged with each other. As to the conventional adhesive compositions,slurry-like liquefied or paste-like adhesive compositions made bydispersing micro-capsules enclosing a reactive adhesive and a resinserving as a binder in an organic solvent or water are disclosed inJapanese Pat. Publication SHO 45-11051(B), Japanese Pat. Publication SHO54-1737(B), Japanese Pat. Publication SHO 52-46339(B), Japanese Pat.Appln. Public Disclosure SHO 1-27684(A), and Japanese Pat. Appln. PublicDisclosure SHO 1-128918(A).

These adhesive compositions are aimed at strengthening the mutualadhesive force of the screw members by destroying the micro-capsuleswhen engaging the screw members to permit the adhesive to flow out oftile micro-capsules.

However, these adhesive compositions with which the thread contact facesof the screw members are coated are required to be dried. Thus, if theadhesive composition contains an organic solvent, it entails a sanitaryproblem of generating the gas of the organic solvent in a dryingprocess.

Furthermore, in the case of using the composition containing water, thedrying process which is carried out at an ordinary temperature takesmuch time, and therefore, requires heating treatment, thereby leading toa problem of losing the stability in preservation of the reactiveadhesive contained in the micro-capsules.

On the other hand, Japanese Patent Publication HEI 3-8393 discloses anadhesive composition with the object of carrying out the drying processat room temperature for a short time, which composition is made byadding, to a binder such as a monomer or oligomer of a photo-hardeningresin which hardens by the action of radiation of ultra-violet rays orthe like, micro-capsules containing an opaque filler, a photo-initiatorwhich starts polymerization of the monomer or oligomer when exposing themonomer or oligomer to the radiation, and the polymer thus obtained orits free-radical polymerization initiator which starts polymerization ofthe oligomer and/or its activator.

Since this adhesive composition has the opaque filler contained in thebinder composed of the photo-hardening resin, the radiation such asultraviolet rays does not reach deep inside the binder, and therefore,only the surface part of the binder which is exposed with theultraviolet rays is polymerized by the photo-initiator. In this state,only the surface part of the adhesive composition is hardened in theform of a film with the inside part kept in its paste state containingthe micro-capsules.

That is to say, the adhesive applied to the thread contact face has itsinside part kept in its paste state covered with a film layer.Therefore, the tightening resistance generated when thrusting a screwmember into its counterpart at the outset lessens. By further screwingup, the micro-capsules are broken to cause the polymerization initiatoror its activator to flow out of the micro-capsules so as to subject thepolymer, oligomer, and monomer to polymerization reaction with thepolymerization initiator or its activator. Consequently, the effects ofsticking and sealing up the screw members are heightened.

However, if the thread contact face of the screw member is left coatedwith the aforenoted adhesive composition for a long time, a part yet tobe hardened of the adhesive composition will be hardened owing tosunlight or heat. This adhesive composition entails a disadvantage suchthat, even when the polymerization initiator or its activator comes outby tightening up the screw member to break the micro-capsules, nopolymerization reaction takes place, and consequently, the effects ofsticking and sealing up the screw members cannot be brought about.

In addition, since the aforesaid film contains an inorganic filler, itis disadvantageously fragile, so that a paste-like part yet to behardened of the adhesive composition may come out when carrying thescrew member such as a bolt in the stage of distribution.

DESCRIPTION OF THE INVENTION

In light of the above, this invention provides an adhesive compositionfor being applied to at least one of thread contact faces of screwmembers so as to stick said thread contact faces to each other inengaging the screw members with each other, which is characterized inthat micro-capsules enclosing at least a reactive monomer of a reactiveadhesive composition comprising said reactive monomer, polymerizationinitiator of said monomer and an activator of the aforementionedpolymerization initiator, which is added at need, is dispersed in abinder comprising a photo-hardening resin composition.

PREFERRED MODES FOR EXECUTING THE INVENTION

One embodiment of the adhesive composition according to this inventionwill be described hereinafter.

The adhesive composition according to this invention includes: (1) anadhesive composition in which micro-capsules separately containing areactive monomer and a polymerization initiator are dispersed in abinder comprising a photo-hardening resin composition, (2) an adhesivecomposition in which micro-capsules containing a reactive monomer and apolymerization initiator and micro-capsules containing an activator aredispersed in a binder comprising a photo-hardening resin composition,(3) an adhesive composition in which micro-capsules containing areactive monomer and a polymerization initiator and micro-capsulescontaining a reactive monomer and its activator are dispersed in abinder comprising a photo-hardening resin composition, (4) an adhesivecomposition in which micro-capsules containing a reactive monomer and apolymerization initiator are dispersed together with an activator in abinder comprising a photo-hardening resin composition, (5) an adhesivecomposition in which micro-capsules containing a reactive monomer andits activator and micro-capsules containing a polymerization initiatorare dispersed in a binder comprising a photo-hardening resincomposition, (6) an adhesive composition in which micro-capsulescontaining a reactive monomer and its activator are dispersed togetherwith a polymerization initiator in a binder comprising a polymerizationinitiator in a binder comprising a photo-hardening resin composition,and (7) an adhesive composition in which micro-capsules containing areactive monomer are dispersed together with a polymerization initiatorand/or its activator in a binder comprising a photo-hardening resincomposition.

Also, in place of the photo-hardening resin composition mixed with thepolymerization initiator or its activator as noted above, aphoto-hardening resin composition containing a functional group of apolymerization initiator or its activator may be used. For instance, aphoto-hardening resin composition containing an amino group can be used.

As the reactive monomer used herein, there can be enumerated a reactivevinyl monomer or its oligomer, preferably an acrylic ester monomer orits oligomer, or a methacrylic ester monomer or its oligomer. Also, anepoxy resin can be used.

As the polymerization initiator of the reactive monomer, a radicalgenerator, e.g. peroxide such as benzoyl peroxide can be used in a casethat the monomer is an acrylic adhesive agent. As the activator of thepolymerization initiator, there are amine serving as a redox catalyst ofthe peroxide or salicylic acid derivative.

In a case that the monomer is an epoxy adhesive agent, amine andsalicylic acid may be enumerated as the polymerization initiator of themonomer.

On the other hand, the photo-hardening resin composition used as abinder is obtained by adding a photo-initiator to the well-known resinwhich is hardened by ultraviolet rays.

By way of example, there may be enumerated (1) a composition in which areactive vinyl monomer, preferably an acrylic ester monomer ormethacrylic ester, contains a photo-polymerization initiator such asbenzophenone, and (2) a composition in which an epoxy resin contains aphoto-polymerization initiator such as onium salt.

Moreover, various kinds of reactive vinyl monomers, epoxy resins andphoto-polymerization initiators have been known, and should not beunderstood as limitative in this invention.

Also, an adhesive composition capable of reducing the resistanceinvolved in tightening up the engaged screw members can be produced byusing a photo-hardening resin serving as a binder, such as flexible orrubber-like elastic material. Instead, if a resin having a high glasstransition temperature is used, an adhesive composition having greatheat-resistance can be produced.

The ratio of the binder composed of the photo-hardening resin to themicro-capsules in the reactive adhesive according to this invention is70% or less in the total amount of the adhesive composition of thisinvention. If it is over 70%, sufficient adhesive power cannot beobtained.

According to this invention, a filler, lubricating agent, and/orcoupling agent can be added to the adhesive composition to providechemical resistance, high adhesive power, and good lubricatingproperties.

As is plain from the foregoing, according to this invention, since atleast the monomer in the reactive adhesive components is enclosed in themicro-capsules, polymerization reaction is achieved by the action of thepolymerization initiator or its activator when the micro-capsules arebroken by tightening up the engaged screw members applied with theadhesive composition to cause the monomer to come out of themicro-capsules. Thus, locking and sealing-up of the engaged screwmembers can be fulfilled reliably.

In addition, since the photo-hardening resin composition is used as abinder, the thread contact faces of the screw members can be coated in ashort time with the binder including the micro-capsules and soonhardened by being exposed to radiation such as ultraviolet rays at roomtemperature without being heated. Thus, the adhesive composition of thisinvention is advantageous from the standpoint of sanitation because itcontains no organic solvent, and it does not damage the preservation andstability of the reactive adhesive agent in the micro-capsules becauseit is not subjected to heat treatment, thereby to enable the screwmembers to be stuck to each other at a low cost.

Moreover, since the photo-hardening resin composition serving as abinder is completely hardened to preserve and stabilize themicro-capsules, a paste-like part yet to be hardened of the adhesivecomposition does not come out of the micro-capsules when carrying thescrew member applied with the adhesive composition in the stage ofdistribution. Besides, the resistance generated in tightening up theengaged screw members can be maintained uniform, the scattering intightening force of the screw members can be eliminated.

The embodiments of this invention will be described hereinafter.

EMBODIMENTS 1-3

A processed bolt was obtained by being applied with an adhesivecomposition obtained by mixing, at the ratio shown in the followingTable 1, and dispersing micro-capsules #1 [capsules enclosing bisphenolA dimethacrylate and a radical generator], micro-capsules #2 [capsulesenclosing bisphenol A dimethacrylate and DMPT (N,N-dimethyl-P-toludine:activator)] in THREE BOND 3057D [UV-hardening acrylic resin containingphoto-polymerization initiator made by THREE BOND CO., LTD.], and then,being exposed to UV rays (integral dose: 600 mJ/cm²).

The bolt thus obtained was provided with two flat washers and tightenedup in a nut with 29.4 N.m. Then, the breaking torque was measured afterthe bolt was held tightened for 24 hours at room temperature.

Comparative Example 1

The breaking torque of an unprocessed bolt provided with two flatwashers and engaged with a nut was measured by tightening up the boltwith 29.4 N.m.

EMBODIMENTS 4-5

The breaking torque was measured in the same manner as those inEmbodiments 1-3 noted above, using an adhesive composition obtained bymixing THREE BOND 3057D with the micro-capsules #1 mentioned above, anactivator [salicylic acid derivative and DMPT(N,N-dimethyl-P-toluidine)] at the ratio shown in the following Table 1.

EMBODIMENT 6

There was used a bolt applied with an adhesive composition obtained bymixing THREE BOND 3057D with the micro-capsules #3 [capsules enclosingbisphenol A epoxy resin], aromatic diamine [polymerization initiatormade by NIPPON KAYAKU CO., LTD.] and a salicylic acid derivative(activator) at the ratio shown in the following Table 1. The breakingtorque was measured by tightening up the bolt in the same manner asthose in Embodiments 1-3 except that the bolt was held tightened at roomtemperature for 72 hours.

EMBODIMENT 7

The breaking torque was measured in the same manner as those inEmbodiments 1-3 except that SINX (UV-hardening epoxy resin containing aphoto-polymerization initiator made by THREE BOND CO., LTD.) was used asa binder.

EMBODIMENT 8

The breaking torque was measured in the same manner as that inEmbodiment 4 except that SINX was used as a binder.

EMBODIMENT 9

The breaking torque was measured in the same manner as that inEmbodiment 6 except that dialkylamino-acrylamide (UV-hardening epoxypolymerization initiator) and DAROCURE 1173 (photo-polymerizationinitiator made by MERCK JAPAN LTD.) were used as a binder. The measuredbreaking torque data obtained in the aforementioned Embodiments andComparative Examples will be shown in Table 1 below. In Table 1, thecomponent A means a component for forming a coating film, and thecomponent B means a component serving as an adhesive agent.

                                      TABLE 1                                     __________________________________________________________________________                                           Embodi-                                                                             Embodi-                                                                            Embodi-                                                                             Comparative                                                  ment 1                                                                              ment 2                                                                             ment 3                                                                              Example               __________________________________________________________________________                                                            1                     Binder                                                                             Photo-hardening                                                                        THREE BOND3057D (UV-hardening acrylic resin                                                            70    50   30    --                         resins   made by THREE BOND CO., LTD.)                                   Capsules                                                                           Polymerization                                                                         Micro-capsules #1 (enclosing                                                                           15    25   30    --                    enclos-                                                                            initiator                                                                              Bisphenol A dimethacrylate + Radical generator)                 ing: Activator                                                                              Micro-capsules #2        15    25   30    --                                  (enclosing Bisphenol A dimethacrylate + DMPT)                   Breaking torque (N · m)         31.1                                                                                33.6                                                                               35.1                                                                                23.5                __________________________________________________________________________                                     Embodi-                                                                            Embodi-                                                                            Embodi-                                                                            Embodi-                                                                            Embodi-                                                                            Embodi-                                              ment 4                                                                             ment 5                                                                             ment 6                                                                             ment 7                                                                             ment                                                                               ment                __________________________________________________________________________                                                              9                   Binder                                                                             Photo-hard-                                                                          THREE BOND3057D (UV-hardening                                                                      50   50   50   --   --   --                       ening resins                                                                         acrylic resin made by THREE                                                   BOND CO., LTD.)                                                        Photo-hard-                                                                          SINX (UV-hardening epoxy resin                                                                     --   --   --   50   50   --                       ening resins                                                                         made by THREE BOND CO., LTD.)                                          Photo-hard-                                                                          Dialkylamino-acrylamide (UV-hardening                                                              --   --   --   --   --   50                       ening resins                                                                         epoxy polymerization initiator)                                               DAROCURE1173 (Photo-initiator made by                                                              --   --   --   --   --    1                              MERCK JAPAN LTD.)                                                      Activator                                                                            DMPT (N,N-dimethyl-P-toluidine)                                                                    --    1   --   --   --   --                              (Acrylic polymerization activator)                                            Salicyic acid derivative (acrylic                                                                   2   --    2   --    2   --                              resin + Epoxy polymerization initiator)                                Polymeriza-                                                                          Aromatic diamine (epoxy resin made by                                                              --   --   15   --   --   --                       tion initiator                                                                       Nippon Kayaku CO., LTD.)                                          Capsules                                                                           Polymeriza-                                                                          Micro-capsules = 1 (enclosing Bisphenol                                                            50   50   --   25   50   --                  enclos-                                                                            tion initiator                                                                       A dimethacrylate + Radical generator)                             ing  Primary                                                                              Micro-capsules = 3   --   --   50   --   --   50                       components                                                                           (enclosing Bisphenol A epoxy resin)                                    Activator                                                                            Micro-capsules = 2 (enclosing Bisphenol                                                            --   --   --   25   --   --                              A dimethacrylate + DMPT)                                          Breaking torque (N · m)   36.8                                                                                35.5                                                                              51.0                                                                               38.2                                                                               41.7                                                                               53.7              __________________________________________________________________________

Test of preservation and stability

After a bolt coated with the adhesive composition used in Embodiment 2was left outdoors for one month and further left in an atmosphere at 40°C. for one month, the bolt was provided with two flat washers and kepttightened with 29.4 N.m for 24 hours. Thereafter, the breaking torquethereof was measured, consequently to obtain a good result as shown inTable 2 below.

                  TABLE 2                                                         ______________________________________                                        Conditions       Breaking Torque (N · zm)                            ______________________________________                                        Blank            33.6                                                         Left outdoors for 1 month                                                                      33.5                                                         40° C. × 1 month                                                                  33.6                                                         ______________________________________                                    

INDUSTRIAL APPLICABILITY

Since at least the reactive monomer in the reactive adhesive componentsis enclosed in the micro-capsules, polymerization reaction is achievedby-the action of the polymerization initiator or its activator when themicro-capsules are broken by tightening up the engaged screw membersapplied with the adhesive composition to cause the monomer to come outof the micro-capsules. Thus, locking and sealing-up of the engaged screwmembers can be fulfilled reliably.

We claim:
 1. An adhesive composition for application to at least onethreaded face of contacting screw members in order to fixedly adhere thethreaded contacting faces of the screw members which engage each other,which consists of microcapsules, which enclose (1) reactive monomersconsisting of at least one acrylic ester monomer, an oligomer of theacrylic ester monomer, a methacrylic ester monomer or an oligomer ofsaid methacrylic ester monomer, and (2) a peroxide serving as apolymerization initiator for said monomers, dispersed in (3-1) a binderconsisting of acrylic ester monomers or methacrylic ester monomers as aphotohardening resin composition and a photopolymerization initiator forsaid monomers or (3-2) a binder consisting of epoxy resins andphotopolymerization initiator for the epoxy resin with (4) an amine orsalicylic acid derivative which serves as an activator for saidperoxide, said binder being completely hardened when external lightpenetrates therethrough, thereby fixing the microcapsules in thehardened binder.
 2. The adhesive composition of claim 1, wherein saidamine is N,N-dimethyl-p-toluidine, and said microcapsules enclose amixture of said amine and acrylic ester monomer which are dispersed insaid binder.
 3. The adhesive composition of claim 1, wherein the amountof binder in the adhesive composition is no more than 70% of the totalweight of components of the adhesive composition.
 4. An adhesivecomposition for application to at least one threaded face of contactingscrew members in order to fixedly adhere the threaded contacting facesof the screw members which engage each other, which consists ofmicrocapsules, which enclose (1) reactive monomers consisting of atleast one acrylic ester monomer, an oligomer of the acrylic estermonomer, a methacrylic ester monomer or an oligomer of the methacrylicester monomer and (2) peroxides serving as a polymerization initiatorfor said monomers, dispersed in (3) a binder consisting of acrylic estermonomers or methacrylic ester monomers having an amino group, saidmonomers being a photohardening resin composition, and (4) aphotopolymerization initiator, said binder being completely hardenedwhen external light penetrates therethrough, thereby fixing themicrocapsules in the hardened binder.
 5. An adhesive composition forapplication to at least one threaded face of contacting screw members inorder to fixedly adhere the threaded contacting faces of the screwmembers which engage each other, which consists of (1) microcapsules,which enclose an epoxy resin, dispersed in (2) a binder consisting of anamine or salicylic acid derivative which serves as an activator for saidepoxy resins and (3) acrylic ester monomers or methacrylic estermonomers, which are a photohardening resin composition, and (4) aphotopolymerization initiator for said monomer, said binder beingcompletely hardened when external light penetrates therethrough, therebyfixing the microcapsules in the hardened binder.
 6. An adhesivecomposition for application to at least one threaded face of contactingscrew members in order to fixedly adhere the threaded contacting facesof the screw members which engage each other, which consists of (1)microcapsules, which enclose an epoxy resin, dispersed in (2) a binderconsisting of acrylic ester monomers or methacrylic ester monomershaving an amino group, the monomers being a photohardening resincomposition, and (4) a photopolymerization initiator for said monomers,said binder being completely hardened when external light penetratestherethrough, thereby fixing the microcapsules in the hardened binder.